Photovoltaic (PV) maximum power point tracker (MPPT) is compulsory in PV systems to improve its output power and efficiency. Conventional techniques can track the maximum power under uniform irradiances efficiently and accurately. Nevertheless, in case of partial shading conditions where multiple peaks are generated, these conventional techniques may stick at any local peak of the P–V curve of the PV energy systems. Metaheuristic techniques have been applied to PV energy systems to overcome this limitation, where most of these techniques can catch the global MPP (GMPP) easily and efficiently. In case of dynamic change of partial shading, most of these techniques need reinitialisation to disperse the search agents to look again for a new position and value of GMPP. This study introduces a brief description, assessment and evaluation for these techniques. In addition, it proposes a novel assessment criterion based on grade point average for evaluating and ranking the 20 famous metaheuristic and hybrid GMPP techniques. This evaluation methodology can help researchers, designer and decision maker to choose the best option for MPPT of dynamic change of partially shading PV energy systems.

Partial shading (PS) condition has a negative effect on the shaded photovoltaic (PV) modules/arrays itself. In addition, it reduces the output power generated considerably. The PV system configuration represents one of the effective solutions to alleviate the PS effects and extract the global maximum power (GMP) available from the partially shaded PV (PSPV) system. This study introduces a detailed performance analysis and comparisons of four proposed PV system configurations [module integrated converter (MIC), multi-strings interfaced interleaved boost converter (MSIBC), multi-arrays interfaced IBC and single array single converter (SASC)] in terms of output power generated and mismatch loss (MML) index. The selection of the best PV system configuration, which not only mitigates the PS effects but also extracts the GMP available from the PSPV system, depends on a trade-off between the generated power, cost and complexity before judging which one is preferable. Although the MIC PV system has the highest output power generated (33 kW) and MML (100%), it increases the PV system complexity. Whereas, MSIBC has the second highest output power generated (28 kW) and MML compared to MIC. SASC has the lowest generated power and MML among the four configurations. The finding proves that MSIBC has superior performance compared to the other PV system configurations considering both the technical and economic assessment.

Photovoltaic (PV) plants operating under the partial shade condition show an imbalance in the array irradiance and produce less output power. To counteract this problem, reconfigurable PV array or dynamic PV array (DPVA) for changing the inter-connections of PV modules to balance the irradiance distribution has been proposed previously. This study introduces a new strategy, the maximum and minimum (M²) algorithm, to identify global maximum irradiance configuration with a minimal number of interchanges among the PV modules. For the implementation of DPVA, this study introduces a double pole double throw (DPDT) switch network (SN) with less switch-count compared to a conventional SN. Simulations of PV array have been carried out on a 9 × 9 size PV array. Results are compared with the previously reported algorithms. Further, cost–benefit analysis of a 10 kW_P grid-tied DPVA plant has been presented. Experimental tests on 4 × 2 size DPVA under different shade conditions are conducted to validate the proposed algorithm and DPDT SN.

In this paper, a comparative study of modulation techniques used in a transformerless H-bridge neutral point clamped (HB-NPC) multilevel inverters is presented. Transformerless inverters, usually found in photovoltaic (PV) applications, are more efficient and economically affordable than isolated systems. Nevertheless, they may cause leakage ground currents. The latter are produced by the stray capacitances formed between the PV panel frame and the ground path. There are different ways to overcome the leakage ground current issue in transformerless topologies, for instance using topologies that generate almost zero leakage currents, by using adequate modulation techniques, by inserting additional filters, and by using adequate control schemes, among others. The comparative study, considers five modulation strategies, namely, level-shifted pulse-width modulation (PWM), phase-shifted PWM, three-level PWM, two sectors hybrid PWM and six sectors hybrid PWM. As it will be demonstrated through the common-mode model analysis, the three last modulations strategies are aimed at alleviating the leakage ground current issue. In this study, the two sectors hybrid PWM and the six sectors hybrid PWM are proposed. These modulation techniques lead to obtaining five output voltage levels keeping the RMS value of the leakage currents bounded for the transformerless HB-NPC inverter.

This study presents a year-long comprehensive performance analysis of four distinct solar photovoltaic (SPV) system configurations with central inverter, micro inverter, fixed axis structure and dual axis sun tracker (DAST) structure installed at the Indian Institute of Technology Kharagpur, West Bengal, India. Technical and economic performance indices are used to analyse the impact of inverter technology and DAST structure using field data of one year. Specifically, technical parameters specified by IEC 61724 are used to compare simulated results with field data from June 2017 to May 2018. The difference between the simulated and measured values of all the configurations is mostly attributed to the variation in solar irradiance and module temperature data. For simulation study, daily and monthly average values are considered while daily instantaneous data are used for measured values. Comparison of measured values through energy yield, capacity factor and performance ratio (PR) indices has confirmed the superiority of dual axis micro inverter system configuration. Additionally, the impact of seasonal variation on PR values for all four system configurations is also analysed. Economic performance for 25 years of project life using payback period, net present value and levelised cost of energy indices concludes dual axis central inverter system configuration as the most economical.

This paper proposes a new hybrid frequency control strategy for doubly fed induction generator (DFIG)-based wind turbines (WTs) to simultaneously provide short-term and long-term frequency regulation support to the connected power system. The kinetic energy stored in the rotating mass and the mechanical power reserve of the WT are coordinately configured to participate in frequency recovery at both primary and secondary stages. A frequency response model (FRM) is also derived to analyse the mutual interactions between WTs and the power system. Based on the FRM, the impacts of relevant parameter variations on the overall system stability can be investigated through Nyquist criterion and modal analyses and the stable operation range of proposed strategy could be easily identified. Theoretical and numerical results have both verified the effectiveness of the proposed control strategy and its advantages over existing methods.

Standalone hybrid remote area power systems, also known as microgrids (MGs), can provide reasonably priced electricity in geographically isolated and the edge of grid locations for their operators. To achieve the reliable operation of MGs, whilst consuming minimal fossil fuels and maximising the penetration of renewables, the voltage and frequency should be maintained within acceptable limits. This can be accomplished by solving an optimisation problem. Floating-point genetic algorithm (FP-GA) is a heuristic technique that has a proven track record of effectively identifying the optimal solutions. However, in addition to needing appropriate operators, the solver needs a fitness function to yield the most optimal control variables. In this study, a suitable fitness function is formulated, by including the operational, interruption and technical costs, which are then solved with an FP-GA, with different combinations of operators. The developed fitness function and the considered operators are tested for the non-linear optimisation problem of a 38-bus MG. Detailed discussions are provided on the impact, which different operators have upon the outcomes of the fitness function.

This paper addresses a framework for expansion planning of an active distribution network (ADS) that supplies its downward active microgrids (AMGs) and it participates in the upward wholesale market to sell its surplus electricity. The proposed novel model considers the impact of coordinated and uncoordinated bidding of AMGs and demand response providers (DRPs) on the optimal expansion planning. The problem has six sources of uncertainty: upward electricity market prices, AMGs location and time of installation, AMGs power generation/consumption, ADS intermittent power generations, DRP biddings, and the ADS system contingencies. The model uses the conditional value at risk (CVaR) criterion in order to handle the trading risks of ADS with the wholesale market. The proposed formulation integrates the deterministic and stochastic parameters of the risk-based expansion planning of ADS that is rare in the literature on this field. The introduced method uses a four-stage optimisation algorithm that uses genetic algorithm, CPLEX and DICOPT solvers. The proposed method is applied to the 18-bus and 33-bus test systems to assess the proposed algorithm. The proposed method reduces the aggregated expansion planning costs for the 18-bus and 33-bus system about 44.04% and 11.82% with respect to the uncoordinated bidding of AMGs/DRPs costs, respectively.

The efficiency of solar cell depends on how the different portions of the solar spectrum are converted to electric energy. The efficiency of solar cell can be increased by using multi-solar cells in tandem configuration or tandem solar cell. The device structure and material choice of tandem solar cell can affect their efficiency. Incorporating quantum well in the solar cell structure also affects their efficiency. This work proposed a new solar cell structure with efficiency 47%, which is very promising. Different materials of the cell and the embedded quantum well will help to increase the efficiency of this solar cell. The fabrication of the cell is less complicated than other promising solar cell because of single quantum well structure. Comparison with other published work also shows the improved performance of this cell.

Analytical modelling of photovoltaic (PV) array is crucial for studying the current–voltage (I–V) characteristic of PV array and maximum power point tracking. A PV array model generally contains some undetermined parameters and the values of the parameters cannot be measured by sensors. It is difficult to correctly determine those model parameters. They should be estimated based on experimental data. Since the experimental data gathered from the solar panel equipment usually contain random and gross errors, a robust parameter estimation method, correntropy-based parameter estimation (C-PE) is proposed for PV array model considering partial shading condition here. First, the theoretical model of PV array considering partial shading condition is investigated. Second, compared with the most common estimator, weighted least squares (WLS), robustness of the proposed correntropy estimator is analysed by using influence function (IF), and then C-PE method is developed for the PV array model. The WLS-based parameter estimation (WLS-PE) and C-PE methods are used in the simulation example. The results show that the C-PE method is more robust than WLS-PE method. Finally, the experimental data of PV array under ideal condition and partial shading condition are also used to demonstrate the feasibility and effectiveness of C-PE method.

As the only power output channel of wind farms, wind-powered outgoing lines carry the risk of reclosing to faults as an applied single-phase reclosing scheme recloses the outgoing line after a fixed time without distinguishing transient and permanent faults. Although various transient-fault identification (TFI) methods were proposed for conventional power transmission lines with shunt reactors, they can be hardly utilised on wind-powered outgoing lines with shunt reactors due to the influence of outgoing line complex working conditions and wind farms inconsistent output power. In this study, reactive power was calculated using the instantaneous power algorithm to obtain the equivalent reactance of the outgoing line faulty phase shunt reactor. Then, a TFI method for the outgoing lines with shunt reactors based on online parameter determination was proposed, a relevant adaptive single-phase auto-reclosing (ASPAR) scheme was established. Finally, the validity and feasibility of the proposed TFI method and ASPAR scheme were verified by conducting simulation experiments on the software PSCAD/EMTDC. The experiments confirmed that the proposed ASPAR scheme can achieve immunity to changes in fault location and transition resistance, and are therefore suitable for inconsistent output power of wind farms and complex working conditions of outgoing lines.

With the increasing integration of wind power and demand response into power system, the complex uncertainties from supply-side and demand-side have brought great challenges to daily operation of the power system. It is essential for enabling a comprehensive and adequate consideration of the manifold uncertainties in the grid. In this study, information granule chance constraint goal programming (IGCCGP) is proposed by a combination of chance constraint goal programming and information granule to provide a uniform representation of the multifaceted uncertainties. Leveraging on IGCCGP, the reserve constraints and branch flow constraints for accommodating the complex uncertainties in the grid are developed and the economic dispatch model considering the combined uncertainties from both supply-side and demand-side is established. To accelerate model solutions without losing much of model accuracy, the deviation in the IGCCGP is transformed to a deterministic equivalent and the optimal schedule is obtained by a mixed linear integer programming. Finally, a computational study is illustrated in the IEEE 39-bus system to verify the efficiency of the proposed method.

Wind integration studies often focus on the capacity value of wind power without considering Unit Commitment and Economic Dispatch or resolving requirements for ancillary services. Here, a novel method for simulating wind power time series with sufficient temporal span to support capacity studies and temporal resolution to support UCED studies is developed. Wind speed time series (WSTS), with 6 h temporal and 0.7 × 0.7 degree spatial resolutions, are extracted from the ECMWF-interim reanalysis, interpolated, scaled, and imputed so that they are representative of a point wind speed measurement with a 5 min temporal resolution. Imputation is made using a wavelet multi-resolution analysis approach that ensures temporally consistent correlations while accounting for heteroskedasticity. WSTS are transformed to power using wind power plant power curves, low-pass filters, and a Markov Chain model of operational efficiencies. The wind power model is validated using a set of measurements made at wind power plants (WPPs) in New Zealand and used to simulate power time series for 2 GW portfolios of WPPs representing compact, disperse, diverse, and business-as-usual portfolios. Metrics for dependability, variability, and predictability are applied to quantify the benefits of spatial diversification.

As the running time of a wind turbine generator unit (WTGU) increases, the ageing and wear of its components will be aggravated gradually, which leads to deterioration of its operation condition. In order to ensure the safe and stable operation of WTGU and prolong its service life, it is of great significance to know the health condition of the WTGU and reasonably arrange maintenance. Based on the structure of the WTGU and the operation principle of the wind turbine generator (WTG), the condition assessment indexes of WTG were built, and the factors influencing the assessment index were determined. The relationship function between the assessment indexes and their influencing factors was established by using the least square support vector machine, which was used to determine the dynamic limitation of condition assessment index of WTG. The dynamic weight of each assessment index was used to characterise the influence of deterioration degree of different components on WTG conditions. Then the health conditions of WTG were evaluated using a similar cloud and fuzzy comprehensive assessment method separately. Finally, the proposed methods were verified by two examples including a direct-drive permanent magnet wind generator and a doubly-fed wind generator.

Recently, renewable energy sources such as wind turbines and solar photovoltaics have been increasingly applied in power systems to support inflated load demands. These renewable sources may be placed at locations that provide higher controllability of inter-area oscillations than those of conventional synchronous generators. Thus, an improved damping effect from such renewables can be expected. On the other hand, the signal selection of the wide-area damping controller (WADC) is normally conducted at an operating point. The strength of the input–output pairs of the WADC will consequently change according to the system operations. This study presents a WADC of wind and solar power sources using probabilistic signal selection. After selecting the most suitable input–output pairs, the control parameters of WADC are optimised using a robust control strategy and multiple-pole placement at several operating points. The designed WADC is evaluated by small-signal and transient stability studies in the IEEE 50-machine 145-bus system to guarantee the stabilising effect of the proposed WADC of wind and solar compared to that of the conventional WADC of synchronous generators.

This paper is aimed at presenting a numerical method for calculating the transient overvoltage across a wind turbine (WT) struck by lightning. The resulting overvoltage is determined at different points along the WT body using the proposed numerical method. The lightning strike has been simulated by injecting a current impulse to the tested WT. The equivalent circuits of WT components and the mathematical formulas to evaluate the circuit's parameters are presented. This makes it possible to develop π-equivalent RLC networks representing the WT components to write the nodal equations at each discrete time instant. MATLAB software package is used to solve the nodal equations and determine the transient behaviour of the WT. In the laboratory, a high impulse voltage is applied on a small-scale WT to corroborate the proposed method. The calculated overvoltage temporal variations are in good agreement with those measured at different positions along the WT for various grounding resistance values, demonstrating the validity of the proposed method. Further validation is also made by comparing the present simulation with that using PSCAD/EMTDC software package. The overvoltage values increase with the rise of the grounding resistance value. The obtained results are useful for designing WT lightning protection systems.

Nearby lightning strikes are prone to induce overvoltage transients in photovoltaic (PV) modules and in their power conditioning circuitry, which can permanently damage the PV system. Therefore, it becomes important to establish a method for accurate assessment of such transients. To this aim, the authors propose a three-dimensional (3D) semi-analytical numerical method to study the electromagnetic transients caused in PV modules by nearby lightning strikes. The approach bases on a semi-analytical expression of the magnetic vector potential generated by a geometrically complex lightning channel. The proposed method is able to calculate the transient overvoltage in a PV module, both in common and differential-mode, taking also into account capacitive and inductive couplings between the internal circuit and the PV metallic frame. Both modes are required to design the surge protective devices (SPDs) in PV power systems. Comparing to the models in literature, the proposed approach explicitly considers the complex geometry of the lightning channel. Statistical analysis allows assessing the impact of channel geometry by randomly generating a number of likely lightning paths. Results show that the lightning-induced overvoltage in a PV module is highly dependent on factors such as distance to the lightning channel and lightning channel geometry.

It is well-known that performance of photovoltaic (PV) systems can be severely deteriorated when PV arrays are subjected to partial shading conditions, once the traditional techniques used for maximum power point tracking (MPPT) could not operate in the global maximum power point (GMPP). Thus, to overcome this problem and achieve the GMPP, four MPPT techniques bio-inspired in the grey wolf optimisation (GWO) are presented. These MPPT techniques, which are named as GWO, GWO-Beta, GWO-IC (Incremental Conductance), and GWO-P&O (Perturb and Observe), are evaluated and compared to each other by employing a double-stage three-phase grid-connected PV system, which is composed of DC/DC converter and three-phase inverter. Commonly, the DC-bus voltage regulation of double-stage PV systems presents slow dynamic behaviour to avoid disturbances in the currents injected into the grid. As a result, MPPT algorithms suffer with this problem since they must be executed considering this condition. To overcome this problem, a feed-forward control loop (FFCL) is implemented to improve the DC-bus voltage regulation during abrupt solar irradiance changes, as well as accelerating the MPPT algorithms dynamics. By means of extensive experimental and simulation results, the performance and effectiveness of the four MPPT techniques, as well as the FFCL, are evaluated.

Calculation of the static voltage stability margin (SVSM) of power system with high wind-power penetration must consider the uncertain fluctuation of power output from wind farms (WFs). On the basis of a continuous power flow (CPF) and improved affine interval (IAI) algorithm that considers quadratic terms, a new method to calculate the SVSM interval of a power system that considers the uncertain fluctuation intervals of WF output is proposed. Considering the high penetration of wind power, the power variation of the active load, and wind-power fluctuation are assigned by all conventional generators, except the swing generator in the CPF calculation model. In the proposed IAI algorithm, the non-linear second-order sensitivities are considered to obtain a more accurate SVSM interval. With the correlation of different WF output intervals described by relative angles, as well as the independent intervals obtained by decorrelation of the correlated WF output intervals, the SVSM interval is calculated by the CPF and IAI algorithms. Take the IEEE 39-bus system and an actual 964-bus provincial power grid as examples, and compared with Monte Carlo method, the results show that the SVSM interval calculated by the proposed method is more accurate, and the computation time is significantly reduced.

This study presents a new step-up DC/DC converter for bipolar DC microgrids. This relies on utilising a new converter topology which offers bipolar DC outputs with the key features of boosting the input voltage and balancing the output voltages. In addition, the proposed converter can transfer power from output terminals to the input side which leads to energy saving. Due to the microgrid's loading conditions, different modes can be considered, and the operational principles are analysed in details. Applying the circuit average method, the small signal model of the proposed converter is derived. Then the appropriate controllers are designed considering the small signal model of the converter in each mode. Finally, a prototype of the proposed converter has been implemented in the laboratory, and the experimental results have verified the converter's ability to balance the bipolar DC grid's voltages and its capability of transferring power in various microgrid's conditions.